Prevention of corrosion of steel by brine containing dissolved oxygen



Patented Nov. 13, 1951 PREVENTION OF CORROSION OF STEEL BY BRINE CONTAINING DISSOLVED OXYGEN Glenn A. Marsh, Crystal Lake, 111., assignor to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Application October 12, 1949, Serial No. 121,050

7 Claims. 1

This invention relates to a method of reducing the corrosion of ferrous metals used in coniunction with oil drilling and storing apparatus, as for example, the ferrous metals used within the well and those used for storing crude oil. More precisely, the invention embodies a method of inhibiting the corrosion of ferrous equipment used in the handling of brine solutions which may be saturated with air.

It has been found in oil well operations that various constituents of the oil and accompanying water can cause serious corrosion of the equipment. One source of corrosion is the brineair system found in some salt water disposal wells. Inasmuch as the occurrence of the brine is something which cannot be controlled, it is accepted in the system, and various means are taken to reduce-or counteract the rate of corrosion. The simplest technique appears to be the adoption of an inhibitor which is sufllciently cheap to be )0 added to the corrosive system in quantities large enough to maintain an inhibiting concentration.

Accordingly, it is a fundamental object of this invention to provide a method of preventing the corrosion which takes place when brine containing dissolved oxygen contacts ferrous equipment.

A second object of the invention is to provide a method of preventing the corrosion of equipment which contacts brine solutions in the storage of oil, the system then comprising the metal, brine and oxygen.

Other objects and advantages of the invention will in part be obvious and in part appear hereinafter.

The invention, accordingly, comprises a process involving protecting iron or ferrous equipment against corrosion by the addition to the brine solution coming in contact therewith of certain small amounts of salts of alkyl dithiocarbamates, as typified by the sodium salts of the ethyl. methyl and propyl dithiocarbamates, which process includes the several steps to be described and the relationship of one or more of such steps to the other to be exemplified in the method hereinafter described and defined in the claims. I have found that the incorporation of the alkali metal salts of these lower alkyl dithiocarbamates, such as sodium, potassium and lithium salts of the dimethyl, diethyl and dipropyl dithiocarbamates. and their mixtures, into brines containing relatively large amounts of salt and other corrosive materials as they occur in an oil well, prevent corrosion of ferrous equipment by the brine, when it contains dissolved air and when it is contacted with the said ferrous equipment.

The type of brine which will occur in the recovery of oils usually contains a number of salts. including sodium, calcium, and magnesium chlorides, as well as a proportion of carbonate or bicarbonate of sodium.

The use of various inhibitors, such as inorganic salts and organic compounds, in a variety of systerns has been disclosed in the prior art. Typical among the processes involved in the use of various inorganic salts, are those disclosed in the following United States Patents: 2,297,666, of September 29, 1942, Aaron Wachter, Sodium Nitrite in Oil Pipe Lines; 2,153,952, of April 11,1939. Alfred L. Bayes, Sodium Nitrate in Anti-Freeze Solutions; 2,135,1 0, of November 1, 1938. Herman Beekhuis, Sodium Dichromate in Ammonium Nitrate Systems.

Thus, these various publications emphasize that the inhibition of corrosion is an empirical phenomenon and particular situations create their own corrosion problems, which require specific solutions. Although a given corrosion inhibitor may be known to be useful in a certain environment, injection of that inhibitor into what may appear to be an analogous situation will frequently be unsound.

The applicability of the instant invention to the inhibition of corrosion of ferrous materials by brine solutions containing various extraneous compounds will be better understood by reference to the following example and those sum marized in the table:

Example.--The experimental procedure described in connection with the instant example was followed in a number of tests so that the manipulation of the several inhibitors in evaluating their effect would not be present as a variable. An aqueous brine having the following composition and containing the metals as chlorides was used.

Parts per million Na 70,000 Ca 24.000 Mg 4,000 HCO: 200

The pH of this brine, which is the composition characteristic of some Michigan oil fields. was adjusted to 610.1 unit with hydrochloric acid, and the brine saturated with air. To a one quart jar fitted with a rubber stopper and several air vents, 800 milliliters of this brine was added. The steel sample immersed in the brine was a 3% inch length of cold-rolled y x inch strip, which had been carefully cleaned prior to immersion by degreasing, pickling and washing in alcohol and water. The sample thus prepared was polished with steel wool to give it a smooth mirror-like finish. A test strip of this steel was suspended on a glass hook which passed through a small hole at one-end of the test piece; It was found that static and gently aerated solutions gave about the same rate of corrosion so that tests were subsequently made on static solutions.

, To minimize the stirring effect of thermal currents and to give a reproducible temperature, the jars were maintained at about 80 F.- -1.0 F..-

by immersion in a thermostatically controlled Corrosion of Steel in Aerated Brine [Seven-day tests.]

- Weight loss,

Inhibitor (0.1% by wt.) I

sq. m.

Sodium dichromate Sodium nitrite Benzyl diethyl dithiocarbamste... Sodium dieth ldithiocarbamata. Ethyl dibuty dithiocarbamate Nickel diethyl dithiocarbamate Sodium diethyl dithiocarbamate Sodium diethyl dithiocarbamate Sulfur (flowers) 2 Mermptobenzothiazole Dim-butylthiourea I l 0.01% by wt. Dim-butylthiourea and 0.01% Aerosol MA added to brine.

It will be seen from the results reported that most corrosion inhibitors and particularly some of them which have been used in systems similar to that described, have substantially no effect on the rate of corrosion, as indicated by their failure to inhibit corrosion to a noticeable extent. From considerations of the solubility and the convenience in maintaining an effective, economic concentration in solution, the alkali metal salts, such as sodium, potassium and lithium, of the ethyl, methyl and propyl dithiocarbamates are most useful as inhibitors.

A brief analysis of the results summarized in the table shows that a brine solution in contact with steel can be expected to establish a corrosion rate when expressed in terms of a weight loss in a seven-day period of about milligrams for 5 square inches of area.- An effective inhibitor, therefore, within the limits of experimental determination which are about 1 or 2 milligrams, ought to reduce the corrosion rate so that it shows at most as about 1 to 4 milligrams per 5 square inches (or about 1 milligram per square inch). Results reported indicate quite clearly that sodium dichromate, a well-known inhibitor frequently used in oil wells, has little or no effect on thecorrosion rate under the conditions used in these tests. Sodium nitrite, another wellknown inhibitor for hydrocarbon and brine systems, appears to accelerate the corrosion rate by a factor of almost three.

Di-normal butylthiourea, a pickling inhibitor, is not soluble in brine to the extent of 0.01% by weight. In the test listed in the table the dinormal butylthiourea was used in conjunction with a wetting agent, Aerosol MA, which is common practice with slightly soluble pickling inhibitors. As shown in the table, the di-normal butylthiourea was not effective in preventing corrosion of steel by brine.

The comparison of the sodium diethyl dithiocarbamate with other thiocarbamates in the table points out in sharp contrast its unique effectiveness as a corrosion inhibitor in the system defined. The sodium diethyl dithiocarbamate reduces the corrosion rate by a factor of about 5 and even the most closely related compounds do not appear to approach it in effectiveness. For example, ethyl dibutyl, benzyl diethyl and nickel diethyl dithiocarbamate are of no effectiveness in the system.

The amounts to be used for improving the effectiveness of the inhibitor can be above the 0.1 per cent shown in the table, but as a practical aspect of controlling corrosion, it is inadvisable to use an inhibitor in greater concentrations, for where the volumes of the solution to which the inhibitor is added are large, the-cost of the inhibitor can become prohibitive and approach in cost the loss caused by uninhibited corrosion. I have found that useful inhibition is obtained with amounts of dithiocarbamates in the range from 0.001 to about 3 per cent. Similarly, any inhibitor which does not reduce the rate of corrosion by at least one-half is hardly worth using in the solution.

While I do not wish to be bound by the particular theory, it appears that brines having a high chloride content, such as characteristic oil field brines, are always corrosive to iron and steel and particularly in the presence of dissolved oxygen. The corrosion encountered with brine in the presence of chloride ions is severe because they have a deleterious effect on passive films which are formed on iron and steel surfaces. Also, the high electrical conductivity of the brine solution favors the formation of galvanic cells wherever small surface heterogeneities exist, and where dissolved oxygen is available, the corrosion will always continue at a more severe rate. I

Having described my invention, it is to be understood that the examples and data given herewith are to be interpreted as illustrative of the scope and not as limitations thereof.

What is claimed is:

l. The method of protecting ferrous metal surfaces against corrosion by brine containing dissolved oxygen comprising, adding to said. brine as an inhibitor water soluble alkali metal dithiocarbamates selected from the group consisting of methyl, ethyl, and propyl substituted dithiocarbamates in amount sufllcient to effect a material reduction in the corrosiveness of said brine on the metal surface.

2. The method in accordance with claim 1 in which about 0.001 to about 3 per cent of the corrosion inhibitor is added to the brine.

3. The method in accordance with claim 2 in which the corrosion inhibitor is a diethyl dithiocarbamate.

4. The method in accordance with claim 2 in which the corrosion inhibitor is a dipropyl ditlrioinhibiting the corrosive eflects 01 said oxygencontaining brine on ferrous metals including the addition of a corrosion inhibiting amount of an alkali metal salt of a N-dialkyl substituted dithiocarbamate to the fluid mixture, said alkyl substituent being selected from the group consisting of methyl, ethyl and propyl.

7. A method in accordance with claim 6 in which the dithiocarbamate is sodium diethyl dithiocarbamate.

' GLENN A. MARSH.

REFERENCES CITED The following references are of record in the file of this patent:

6 UNITED STATES PATENTS Number Name Date 1,797,402 Calcott et al. Mar. 24, 1931 2,160,880 Loane June 6, 1939 2,238,651 Keenen Apr. 15, 1941 2,453,881 Viles et a1 Nov. 16, 1948 ,474, 3 Viles et al. June 28, 1949 OTHER REFERENCES Thornton-Remedies Studied for Freakish Corrosion, Article in Petroleum Processing, Apr. 1947 pages 273, 275, 276 and 279.

Sheppard1 ipe Line Corrosion-Article in World Oil, June 1949-PipeLine Section-pp.

193, 194, 19a, and 202. 

1. THE METHOD OF PROTECTING FERROUS METAL SURFACES AGAINST CORROSION BY BRIME CONTAINING DISSOLVED OXYGEN COMPRISING, ADDING TO SAID BRINE AS AN INHIBITOR WATER SOLUBLE ALKALI METAL DITHIOCARBAMATES SELECTED FROM THE GROUP CONSISTING OF METHYL, ETHYL, AND PROPYL SUBSTITUTED DITHIOCARBAMATES IN AMOUNT SUFFICIENT TO EFFECT A MATERIAL REDUCTION IN THE CORROSIVENESS OF SAID BRINE ON THE METAL SURFACE. 